This invention relates to head load/unload mechanisms for rotating magnetic memories and, more particularly, to solenoid controlled head load/unload mechanisms for loading and unloading the read/write head or heads of single or double sided floppy disk drives into and out of data transfering relationship with a magnetic recording medium.
Floppy disk drives customarily employ a recording medium comprising a thin, pliant, disk-shaped substrate which has a magnetic oxide surface coating. Such a recording medium is conventionally encased within a protective outer jacket, but there normally are radially extending access slots which pass through the opposing faces of the jacket so that the read/write head or heads of a drive can be compliantly loaded directly against the recording medium to transfer data thereto or therefrom. In operation, the recording medium is inserted into a drive where it is clamped on a spindle for rotation at a substantially constant rate within its protective jacket. The head or heads of the drive are aligned with the access slots in the jacket and are mounted for movement radially of the recording medium so that any selected one of a plurality of concentric data tracks may be accessed. As will be appreciated, a double sided drive provides access to the data tracks on either side of the recording medium, while a single sided drive only has access to the data tracks on one side of the recording medium.
To avoid excessive head/media wear, most single and double sided floppy disk drives have a solenoid controlled head load/unload mechanism for selectively "loading" and "unloading" the read/write head or heads depending on whether the drive is operating in an active data transferring mode or not. When the drive is selected for a data transfer with, say, a host computer, the heads are "loaded" against the recording medium. Otherwise, however, the head or heads are displaced or "unloaded" from the recording medium to prevent any significant head/media wear from occurring, even if the drive is operated for extended periods of time in a standby mode.
Prior solenoid controlled head load/unload mechanisms have generally included means for damping the unloading motion of the head or heads to prevent them from bouncing back into contact with the recording medium. Moreover, it has been suggested that the head/media wear can be further reduced if the loading motion of the head or heads is also damped, but the mechanisms which have been proposed for accomplishing that are not completely satisfactory. For example, one proposal has involved the use of an internally damped solenoid, but cost effective snap action solenoids do not readily lend themselves to internal damping because they generate substantial forces. Another proposal has been based on the use of a dash pot to reduce the velocity of the head or heads as they impact against the recording medium, but that adds an additional component which must be individually aligned with the head/carriage assembly of the drive.